Alligator Study Provides Insight into Dinosaur Hearing

Alligator Hearing Study Provides Insight into Dinosaur Hearing

New research published in the “Journal of Neuroscience” identifies that living Archosaurs – birds and crocodiles make a mental map of sounds in the same way. This suggests that this auditory strategy existed in their common ancestor which has implications for dinosaur research.

Animal brains determine where a sound is coming from, by analysing the minute difference in time it takes audio waves to reach each ear—a cue known as interaural time difference. What happens to the cue once the signals get to the brain depends on what kind of animal is doing the hearing.

An American Alligator – New Research Suggests that Birds and Crocodilians Hear in the Same Way

Scientists have known that birds are exceptionally good at creating neural maps to chart the location of sounds, and that the strategy differs in mammals. Little was known, however, about how alligators process interaural time difference.

A new study of American alligators (Alligator mississippiensis), found that the reptiles form neural maps of sound in the same way birds do. The research by Catherine Carr, a Distinguished University Professor of Biology at the University of Maryland and her colleague Lutz Kettler from the Technische Universität München, was published this week in the “Journal of Neuroscience”.

Most research into how animals analyse interaural time difference has focused on physical features such as skull size and shape, but Carr and Kettler believed it was important to look at evolutionary relationships.

Birds have very small head sizes compared with alligators, but the two groups share a common ancestor, as both Aves (birds) and crocodilians are members of the Archosauria. Archosaurs began to emerge around 246 million years ago and split into two lineages; one that led to alligators and one that led to dinosaurs (and birds). Although most dinosaurs died out during the mass extinction event 66 million years ago, some types of dinosaur survived and we see their descendants all around us today, these are the modern birds.

Carr and Kettler’s findings indicate that the hearing strategy birds and alligators share may have less to do with head size and more to do with common ancestry.

Carr commented:

“Our research strongly suggests that this particular hearing strategy first evolved in their common ancestor. The other option, that they independently evolved the same complex strategy, seems very unlikely.”

To study how alligators identify where sound comes from, the researchers anesthetised forty American Alligators and fitted them with earphones. They played tones for the sleepy reptiles and measured the response of a structure in their brain stems called the nucleus laminaris. This structure is the seat of auditory signal processing. Their results showed that alligators create neural maps very similar to those previously measured in barn owls and chickens. The same maps have not been recorded in the equivalent structure in mammal brains.

The Distinguished Professor added:

“We know so little about dinosaurs. Comparative studies such as this one, which identify common traits extending back through evolutionary time add to our understanding of their biology.”

Everything Dinosaur acknowledges the assistance of a press release from the University of Maryland in the compilation of this article.

The scientific paper: “Neural Maps of Interaural Time Difference in the American Alligator: A Stable Feature in Modern Archosaurs” by Lutz Kettler and Catherine Carr and published in the Journal of Neuroscience.